Circular Aperture - Because aperture blades form a near circle at the wide openings used for low-light shots, spot-light sources have a pleasing circular defocused effect.

Advisory when using DT lenses with full-frame (35mm equivalent) DSLR cameras.Sony a (alpha) lenses with the Digital Technology (DT) designation are ideal for use on APS-C size DSLR cameras and are not recommended for use with full frame DSLR camera bodies (such as the DSLR-A900). Although DT lenses can be used with full frame cameras, they can only realize a maximum of 11MP image size (when using the DSLR-A900), and are not guaranteed to provide accurate Auto Exposure performance.